Epoxy resins crosslinked structure formation

Figure 10.3 Schematic of crosslinked structure formation of an epoxy resin...

Recently, we have developed a real time pulsed NMR(RTPNMR) system(2) controlled by a microcomputer as shown in Figure 3 to study dynamics of structure formation in polymer systems. It has been successfully applied to study crystallization process (3), gelation process(4) and so on. In this paper, application of RTPNMR for characterization of curing process of epoxy resins, polymerization crosslinking process of diacetylenes, and orientation process of liquid crystalline polymers(LCPs) under magnetic field are described. Papers related to the detailed analysis of these data will appear in the near future. EXPERIMENTAL... 

In the conventional curing processes of epoxy resins, the crosslinks developed are of a single strand structure involving ether or amine extension points. The object of this study is the formation of the oxazolidone ring which by reaction of epoxy and isocyanate groups, affords an alternative type of crosslink, which it was anticipated will have a significant influence on the T of the cured epoxy resin. 

There is evidence to suggest that exposure to humid environments, at temperatures above about 60°C can produce permanent damage in epoxy adhesives.Apicella and coworkers have explained this in terms of the formation of microcavities produced by clusters of water molecules. This mechanism of damage is expected to be evident in thermoset resins in which the rigid crosslinked structure does not allow the matrix to relax after microvoid formation. 

A network structure has been shown to influence the moisture-absorption properties of epoxy resins. The diffusion coefficient has, however, been shown to be independent of the degree of crosslinking. It has been further shown that, in the curing of epoxy resins with diamines, curing gave rise to shrinkage in the cured films which, in turn, resulted in the formation of stresses. The extent... 

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